Plant extracts are used for the preparation of drugs, cosmetics, as colorants, spices and food additives. Traditional methods of extraction are distillation, cold pressing or solvent extraction, however the method of extraction can have a significant effect on the quality of the extract, and is closely related to the choice of solvent and conditions of the extraction. Compared to other forms of extraction, supercritical carbon dioxide (CO2) extraction is environmentally friendly, non-toxic, inexpensive, and the CO2 solvent can be easily separated from the extract by evaporation. Moreover, by changing extraction pressure and temperature, the solubility and selectivity of supercritical CO2 for species of interest can be changed to optimize the extraction.
Supercritical (or subcritical) Fluid Extraction (SFE) is the process of separating a desirable extractant from another material where supercritical fluid is the extracting solvent. Because the physical properties of supercritical fluids are close to those of liquids and their transport properties are close to those of gases, supercritical fluids can penetrate into a porous solid material more effectively than liquid solvents. Moreover, after extraction, the solvent can be easily separated from the extract by decreasing the pressure and evaporating the solvent. In an SFE extraction from plants, the matrix is usually solid matrix, but can also be liquid. SFE can be used, for example, for analytical purposes, decaffeination or component removal from a plant material, or collecting desired product such as terpenes or essential oils. The conditions for extraction of oil and other desirable components from plant material is dependent on temperature, pressure, solvent to feed ratio and flow rate, and conditions for extraction vary based on the plant material used.
Carbon dioxide is a widely used supercritical fluid extraction solvent and is sometimes modified by co-solvents such as ethanol or methanol. Carbon dioxide is a gas solvent which will be in liquid form at certain temperature and pressure. Supercritical carbon dioxide (sCO2) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.
Extraction with supercritical fluid CO2 has been used to remove active constituents from foods such as caffeine from coffee beans, and humulene and other flavours from hops (Humulus lupulus). Extraction of desirable oils and active constituents from plants removes plant cell constituents including but not limited to fats, waxes, carbohydrates, proteins and sugars. Cannabis plant material is being used to formulate medicinal compositions and contains sesquiterpenes, terpenes, cannabinoids (THC, CBD, CBN), flavonoids, pigments, sugars, chlorophylls, waxes, lignin, pectins, starches and cellulose. Pharmaceutical-grade cannabis concentrates can be prepared by extracting out the desirable active terpene materials from the non-active matrix plant materials. Supercritical or subcritical CO2 extraction is generally considered the safest and cleanest method of extraction of desirable materials from plants and many compounds can be selectively dissolved into CO2 by varying pressure because extractant solubility in CO2 varies with CO2 extraction pressure. In extraction of cannabis, highly controlled conditions of temperatures of CO2 preserve the integrity of cannabinoids during cannabis oil extraction.
One factor that can influence the extraction rate and yield of extractants from plants is the presence of natural convection in supercritical extractor. Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Supercritical fluids are prone to natural convection because of their very low kinematic viscosity, making them particularly suitable for cyclonic separation.
U.S. Pat. No. 9,132,363 to Joseph describes an extraction apparatus for removing an extracted material from a source material in contact with a process fluid. The apparatus has an extraction vessel, a separation chamber, and a process fluid circulation conduit to direct flow of the process fluid into and out of the extraction vessel. This extractor uses valve-less expansion through an orifice pointed toward the side of separator to restrict flow to cause a rapid decompression to force CO2 from supercritical/liquid to gas.
CO2 functions as a solvent when it is heated or cooled and pushed through plant material at high pressure (supercritical) or low pressure (subcritical). Most CO2 cannabis flower extractions are done in the subcritical phase before it moves on to supercritical phase because it gives a lighter colored extract, fewer waxes and resins, and retains significantly more volatile oils compared to supercritical CO2 extraction. However, without the proper equipment rated for the proper pressures, creating quality CO2 extracted concentrates can be challenging. Effective models of extraction and experimental tests assist to determine the basic mass transfer data necessary for scale-up procedures. The relatively slow diffusion at industrial scale superfluid extraction is often due to the difficulty to setup extraction conditions and to the change of conditions of scale up from laboratory scale to industrial scale.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.